One requirement for next-generation wireless communication systems is to be able to support a high data transmission rate. For this purpose, there is ongoing research, such as MIMO (Multiple Input Multiple Output), CoMP (Cooperative Multiple Point Transmission), or relays, but the most fundamental and stable method is to broaden bandwidth.
However, frequency resources are now in saturation, and various technologies are used to occupy a wide range of frequency bands. To meet demand for a higher data transmission and secure a broader bandwidth, the concept of carrier aggregation (CA) has been introduced which ties a number of bands into a single system and provides a design that may satisfy the basic requirement that each spread band may operate an independent system. At this time, the band which enables each independent operation is defined as a component carrier (CC).
To support increasing transmission capacity, recent communication standards, e.g., 3GPP LTE-A or 802.16m, consider expanding the bandwidth up to 20 MHz or more. In such case, one or more component carriers are aggregated to support the broadband. For example, if a single component carrier corresponds to a bandwidth of 5 MHz, four carriers are aggregated to support the maximum of a bandwidth of 20 MHz. As such, the carrier aggregation system uses multiple component carriers, and may be in this sense referred to as a “multi-carrier system”.
Meanwhile, for efficient communication between a base station and user equipment, feedback of channel state information (CSI) is required. However, in a multi-carrier system, channel state information fed back from the user equipment to the base station is generated for each component carrier of the downlink and may be transmitted through one component carrier of the uplink. In such case, compared with when one carrier is conventionally used for the downlink, more channel state information need to be transmitted through one carrier of the uplink. Accordingly, it is an issue to figure out a method of being able to efficiently transmit the channel state information.